Both focus on the interactions between the poor and the rich. In fact, the word "parasite" is uttered by the rich people in "My Wonderful Life" many times. I'd say that Parasite is darker for sure, and My Wonderful Life is more realistic.
In both these dramas, the main characters husband cheats on them and divorces them. Both the main characters meet someone new and fall in love. The cheating husbands are miserable with their new wives lol